High efficiency blood pump

ABSTRACT

A blood pump can include a pump housing, an impeller, and a hub. The pump housing can be configured to move blood from an inlet to an outlet thereof. The impeller can be housed in the pump housing, have a plurality of blades joined by a central ring, and be radially supported at the central ring by a bearing. The hub can transmit torque to the impeller using a radial magnetic coupling.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/973,593, which is a continuation of U.S. patent application Ser. No.12/899,748, filed Oct. 7, 2010, and issued as U.S. Pat. No. 9,227,001,the entirety of each of which is hereby incorporated by referenceherein.

FIELD OF THE INVENTION

This invention relates to implantable rotary blood pumps.

BACKGROUND OF INVENTION

Some blood pumps mimic the pulsatile flow of the heart and haveprogressed to designs that are non-pulsatile. Non-pulsatile orcontinuous flow pumps are typically rotary and propel fluid withimpellers that span the spectrum from radial flow centrifugal typeimpellers to axial flow auger type impellers.

A common issue encountered by blood pumps is blood damage. The causes ofblood damage are mostly attributed to shear stress and heat generated bythe bearings supporting the impeller and/or shaft seals of externallydriven impellers. Shear stress and/or heat may cause hemolysis,thrombosis, and the like.

A great deal of effort has been devoted to reducing or eliminating blooddamage in rotary blood pumps. One solution to minimizing/eliminatingblood damage is to provide total hydrodynamic support of the impeller.For example, ramp, wedge, plain journal, or groove hydrodynamic bearingsmay be utilized to provide hydrodynamic support in blood pumps.

Additionally, passive permanent magnetic and active controlled magneticbearings can be utilized to provide impeller support in blood pumps.Magnetic bearings may be combined with hydrodynamic bearings to providetotal impeller support in blood pumps.

Some blood pumps provide blood flow utilizing a motor that has a shaftmechanically connected to an impeller. Shaft seals may be utilized toseparate the motor chamber from the pump chamber. However, shaft sealscan fail and generate excess heat allowing blood to enter the motorand/or produce blood clots. Some blood pumps incorporate electric motorsinto the pumping chamber, rather than providing separate motor andpumping chambers. For example, a stator may be provided in the pumphousing and magnets can be incorporated into an impeller to provide apump impeller that also functions as the rotor of the electric motor.

Heart pumps that are suitable for adults may call for approximately 5liters/min of blood flow at 100 mm of Hg pressure, which equates toabout 1 watt of hydraulic power. Some implantable continuous flow bloodpumps consume significantly more electric power to produce the desiredamount of flow and pressure.

High power consumption makes it impractical to implant a power source inthe body. For example, size restrictions of implantable power sourcesmay only allow the implantable power source to provide a few hours ofoperation. Instead, high power consumption blood pumps may provide awire connected to the pump that exits the body (i.e. percutaneous) forconnection to a power supply that is significantly larger than animplantable power source. These blood pumps may require external powerto be provided at all times to operate. In order to provide somemobility, external bulky batteries may be utilized. However,percutaneous wires and external batteries can still restrict themobility of a person with such a blood pump implant. For example, suchhigh power consumption blood pumps have batteries that frequentlyrequire recharging thereby limiting the amount of time the person can beaway from a charger or power source, batteries that can be heavy orburdensome thereby restricting mobility, percutaneous wires that are notsuitable for prolonged exposure to water submersion (i.e. swimming,bathing, etc.), and/or other additional drawbacks.

The various embodiments of blood pumps discussed herein may be suitablefor use as a ventricular assist device (VAD) or the like because theycause minimal blood damage, are energy efficient, and can be powered byimplanted batteries for extended periods of time. Further, these pumpsare also beneficial because they may improve the quality of life of apatient with a VAD by reducing restrictions on the patient's lifestyle.

SUMMARY OF THE INVENTION

The discussion herein provides a description of a high efficiency bloodpump that is energy efficient, causes minimal blood damage, and improvesquality of life.

An embodiment of a blood pump includes a pump housing, wherein the pumphousing provides an inlet and outlet. The blood pump also includes animpeller housed in the pump housing, wherein the impeller is radiallysupported by a first hydrodynamic bearing that provides at least one rowof flow inducing pattern grooves.

Another embodiment of a blood pump includes a pump housing, wherein thepump housing provides an inlet and outlet. The blood pump also includesan impeller housed in the pump housing, wherein the impeller is axiallysupported by a first hydrodynamic bearing that provides at least one rowof flow inducing pattern grooves.

Yet another embodiment of a pump includes a pump housing providing aninlet and outlet and a motor housing, wherein the motor housing houses amotor. The pump also includes an impeller housed in the pump housingthat is radially supported by a hydrodynamic bearing that provides atleast one row of pattern grooves. The pump also provides a magneticcoupling between the motor and the impeller, wherein the magneticcoupling causes the impeller to rotate when the motor rotates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an illustrative embodiment of a pump;

FIG. 2 is a cross-sectional side view of an illustrative embodiment of apump;

FIG. 3 is a cross-sectional top view of an illustrative embodiment of apump;

FIG. 4 is a close up cross-sectional view of an area of an illustrativeembodiment of a pump;

FIG. 5 is a cross-sectional view of an illustrative embodiment of animpeller;

FIG. 6 is a cross-sectional view of an illustrative embodiment of a pumphousing;

FIG. 7 is a cross-sectional view of an illustrative embodiment of amotor housing of a pump;

FIG. 8 is an isometric view of an illustrative embodiment of animpeller;

FIG. 9A-9K are illustrative embodiments of various types of patterngrooves;

FIG. 10A-10D are cross-sectional views of various shapes of patterngrooves;

FIG. 11 is a cross-sectional side view of an illustrative embodiment ofa pump with an axial hydrodynamic bearing;

FIGS. 12A and 12B are top views of illustrative embodiments of impellerswith spiral herringbone grooves and spiral grooves;

FIG. 13 is a close up cross-sectional view of an area of an illustrativeembodiment of a pump with an axial hydrodynamic bearing;

FIGS. 14A and 14B are isometric views of illustrative embodiment ofimpellers with spiral herringbone grooves and spiral grooves;

FIG. 15 is a cross-sectional side view of an illustrative embodiment ofa pump with a conically shaped impeller;

FIG. 16A-16E are isometric views of illustrative embodiments ofconically shaped impellers;

FIG. 17 is a close up cross-sectional view of an area of an embodimentof a pump with a conically shaped impeller;

FIG. 18 is a cross-sectional side view of an illustrative embodiment ofa pump with passive magnetic axial bearings;

FIG. 19 is a cross-sectional top view of an illustrative embodiment of apump with passive magnetic axial bearings; and

FIG. 20 is a close up cross-sectional view of an area of an illustrativeembodiment of a pump with passive magnetic axial bearings.

DETAILED DESCRIPTION

Refer now to the drawings wherein depicted elements are not necessarilyshown to scale and wherein like or similar elements are designated bythe same reference numeral through the several views.

The following detailed description provides an implantable, energyefficient, small, seamless, and magnetically driven blood pump. Theblood pump is capable of operating for extended periods of time on asingle charge. For example, the energy efficient blood pump may besuitable for use with an implanted rechargeable power source or thelike. The pump can be installed pericardially (i.e. near the heart) withless complex surgical procedures. Those skilled in the art willappreciate that the various features discussed below can be combined invarious manners, in addition to the embodiments discussed below. Thescope of the claims is in no way limited to the specific embodimentsdiscussed herein.

FIG. 1 is a top view of an illustrative embodiment of pump 10. Pump 10is formed from pump housing 15 providing inlet 20 and outlet 25 andmotor housing 35. Pump housing 15 is composed of two or more pieces andmay be joined by welding. However, in other embodiments, pump housing 15may be joined by fusing, press fit, threading, screw and elastomericsealing, bonding, fasteners, and/or any other suitable joining method orcombinations of joining methods. Motor housing 35 may be joined to pumphousing 15 by welding, fusing, press fit, threading, screw andelastomeric sealing, bonding, fasteners, and/or any other suitablejoining method or combinations of joining methods. Line A-A passingthrough pump housing 15 indicates the plane from which thecross-sectional view in FIG. 2 is provided.

FIG. 2 is a cross-sectional side view of an illustrative embodiment ofpump 10. Pump housing 15 provides impeller chamber 30 for impeller 75.Impeller chamber 30 has inlet 20 for connection to a fluid source andoutlet 25 for providing fluid to a desired location. Impeller chamber 30is sealed and pressure tight to prevent fluid from entering/exitingimpeller chamber 30 from locations other than inlet 20 and outlet 25.

Motor housing 35 is attached to pump housing 15 to form a fluid and/orpressure tight chamber for motor 40. While motor housing 35 is shown asa separate component from pump housing 15, in other embodiments, pumphousing 15 and motor housing 35 may be combined to form a singlecombined housing. A cross-sectional view of an illustrative embodimentof motor 40 and motor housing 35 of pump 10 is shown in FIG. 7. Inparticular, motor housing 35 is shown separate from pump 10. Motor 40 isentirely contained between pump housing 15 and motor housing 35. A highefficiency electric motor can be utilized, such as an electric motorwith efficiency of about 85% or greater. However, in other embodiments,any other suitable driving means can be utilized. Motor 40 providesshaft 45 with hub 50 mounted to shaft 45. Hub 50 contains one or morepermanent magnets and/or magnetic materials 55. Motor 40 rotates shaft50 causing permanent magnets 55 placed in hub 50 to rotate. In someembodiments, a motor with a useful life of greater than 10 years isutilized. Further, the motor may utilize hydrodynamic bearings withfluid support provided by a fluid other than blood.

A cross-sectional view of an illustrative embodiment of pump housing 15without impeller 75 is shown in FIG. 6. Pump housing 15 may provide anon-ferromagnetic and/or non-electrically conductive diaphragm 60separating impeller chamber 30 from the chamber housing motor 40.Diaphragm 60 defines cavity 70 providing a region for hub 50 to rotatewithin. Additionally, diaphragm 60 may provide cylindrical bearingsurface 65 for impeller 75 to rotate around with hydrodynamic radialsupport. Impeller 75 includes one or more permanent magnets and/ormagnetic materials 80. Permanent magnets 80 allow impeller 75 to bemagnetically coupled to hub 50. This magnetic coupling allows motor 40to cause impeller 75 to rotate when motor 40 rotates hub 50.

Line B-B passing through pump housing 15 indicates the plane from whichthe cross-section view in FIG. 3 is provided. FIG. 3 is across-sectional top view of an illustrative embodiment of pump 10.Impeller 75 is composed of an array of arc shaped segments 90 joined bycentral ring 95. Pump housing 15 has volute 110 feeding the outlet 25.In other embodiments, volute 110 could be omitted from pump housing 15and outlet 25 could have any suitable orientation and shape. Pumphousing 15 is designed in a manner where impeller 75, when rotated,pressures and moves fluid received from inlet 20 to outlet 25.

Permanent magnets 55 in hub 50 and permanent magnets 80 in central ring95 of impeller 75 form a magnetic coupling between the impeller 75 andhub 50. In contrast to radial magnetic bearings that are arranged torepel each other, permanent magnets 55 and 80 are arranged so that theyare attracted to each other. In order to minimize radial loads,permanent magnets 55 and 80 provide a minimal magnetic coupling or justenough of a magnetic coupling to rotate impeller 75 under load. Theattractive force of the magnetic coupling of permanent magnets 55 and 80also provides axial restraint of impeller 75. For example, axialmovement of impeller 75 would misalign permanent magnets 55 and 80. Themagnetic forces of permanent magnets 55 and 80 would restrain andre-align the magnets. Because of the magnetic forces caused by permanentmagnets 55 and 80, axial movement of impeller 75 may cause axial forceto be exerted on shaft 45 and hub 50 of motor 40, which is thentransferred to bearing(s) (not shown) of motor 40.

Permanent magnets 80 may be sufficiently small in size that they have noimpact on the main fluid flow paths of impeller 75, thereby allowing thedesign of impeller 75 to focus on fully optimizing pump efficiency.These benefits can allow pumping efficiencies of greater than 50% to beachieved.

Impeller internal surface 100 of central ring 95 is utilized to form ahydrodynamic bearing between cylindrical bearing surface 65 and impellerinternal surface 100. Impeller 75 is configured to rotate withinimpeller chamber 30 with full radial hydrodynamic support from thehydrodynamic bearing formed by cylindrical bearing surface 65 andimpeller internal surface 100. A cross section view of an illustrativeembodiment of impeller 75 is shown in FIG. 5 and an isometric view of anillustrative embodiment of impeller 75 is shown in FIG. 8, which morethoroughly illustrate the hydrodynamic bearing.

Pattern grooves on impeller internal surface 100 of impeller 75 create ahigh pressure zone when impeller 75 is rotated, thereby creating ahydrodynamic bearing. For example, symmetrical herringbone groovescreate a high pressure zone where the two straight lines of the V-shapegrooves meet or the central portion of the symmetrical herringbonegrooves. The pressure created by the pattern grooves on impellerinternal surface 100 acts as a radial stabilizing force for impeller 75when it is rotating concentrically. While the embodiment shown providessymmetrical herringbone grooves on internal surface 100 of impeller 75,a variety of different groove patterns may be utilized on impellerinternal surface 100 to provide a hydrodynamic bearing, which isdiscussed in detail below. Because low loads are exerted on impeller 75,the radial hydrodynamic bearing formed between cylindrical bearingsurface 65 and impeller internal surface 100 can provide stable radialsupport of impeller 75.

Impeller 75 may be an open, pressure balanced type impeller to minimizeaxial thrust. Impeller 75 is considered to be open because there is noendplate on either side of arc shaped segments 90. Further, impeller 75is considered to be pressure balanced because it is designed to minimizeaxial thrust during the rotation of impeller 75. However, other types ofimpellers may be suitable in other embodiments. Impeller 75 could be anyother suitable blade shape, rotate in the opposite direction, ornon-pressure balanced. For example, other suitable impellers may besemi-open type (i.e. end plate on one side of impeller) or closed type(i.e. end plate on both sides of impeller).

FIG. 4 is a close up cross-sectional view of an area C (see FIG. 2) ofan illustrative embodiment of pump 10. The magnetic coupling transmitstorque from shaft 45 of the motor 40 to impeller 75. In the embodimentshown, permanent magnets 55 and 80 are radially distributed around hub50 and impeller 75. The poles of permanent magnets 55 and 80 arearranged to attract to each other. The attractive force of the magneticcoupling of permanent magnets 55 and 80 provides axial restraint ofimpeller 75. While permanent magnets 55 and 80 are shown as arc shapedlike quadrants of a cylinder, it should be recognized that permanentmagnets 55 and 80 may be shaped in a variety of different manners toprovide the magnetic coupling. For example, one or more ring shapedmagnets polarized with arc shaped magnetic regions, square/rectangularshaped, rod shaped, disc shaped, or the like may be utilized. In themagnetic coupling arrangement shown, permanent magnets 80 are shown inthe internal portion of impeller 75. Internal magnetic couplings,similar to the arrangement shown, can be more efficient than face orexternal type magnetic couplings that place the magnets in the blades ofan impeller or rotor because they have a smaller diameter and less eddycurrent losses. Diaphragm 60, intermediate the coupling, isnon-ferromagnetic and/or non-electrically conductive to minimize eddycurrent losses. For example, couplings with non-electrically conductingdiaphragms such as bio-compatible ceramic, glass or the like, wouldexhibit less eddy current losses than those with electrically conductingdiaphragms.

In one embodiment, motor 40 is of the brushless DC, sensorless, ironcore type electric motor with fluid dynamic bearings. However, in otherembodiments, any suitable type of motor including one or more featuressuch as, but not limited to, brushed, hall-effect sensored, coreless,and Halbach array or any type of bearing such as ball or bushing may beused. Motor housing 35 may include motor control circuitry or beconfigured to operate with remotely located control circuits.

Separating motor 40 from impeller chamber 30 may allow a high efficiencymotor to be utilized. For example, incorporating components into a pumpimpeller to form the rotor of an electric motor may compromise thedesign of the pump impeller resulting in reduced efficiency. Further,designing a rotor and stator that is incorporated into the design of apump may result in an electric motor with large gaps between componentsof the rotor and stator, thereby decreasing the efficiency of the motor.The magnetic coupling arrangements utilized in the embodiments discussedherein allow a highly efficient motor design to be utilized withoutcompromising the design of an efficient pump impeller.

As shown in FIGS. 4-5, a maximum height 320 of the plurality of blades90 overlaps with the internal surface 100, having a height 312, themaximum height 320 being in a direction of an axis 350 of impellerrotation. As shown in FIG. 4, a topmost extent 330 of the plurality ofblades 90 is axially closer to the inlet 20 than is (a) a topmost extent340 of the hydrodynamic bearing and (b) a bottom 332 of the plurality ofblades 90. As shown in FIGS. 12A and 12B, a maximum cross-sectionaldimension 304 of a shape 302 inscribed by all radially innermost edges300 of the plurality of blades 90 is greater than a maximumcross-sectional dimension 310 of the impeller internal surface 100.

FIGS. 9A-9K and 10A-10D illustrate various embodiments of patterngrooves that may be implemented on impeller internal surface 100. Asdiscussed previously, impeller internal surface 100 provides ahydrodynamic journal bearing. For example, impeller internal surface 100may utilize patterned grooves. The pattern grooves may be of any typeincluding, but not limited to, half herringbone (FIG. 9A), dual halfherringbone (FIG. 9B), symmetrical herringbone (FIG. 9C), dualsymmetrical herringbone (FIG. 9D), open symmetrical herringbone (FIG.9E), open dual symmetrical herringbone (FIG. 9F), asymmetricalherringbone (FIG. 9G), continuous asymmetrical dual herringbone (FIG.9H), asymmetrical dual herringbone (FIG. 9I), asymmetrical openherringbone (FIG. 9J), asymmetrical open dual herringbone (FIG. 9K), orthe like. Flow inducing pattern grooves, such as half herringbonepatterns and asymmetrical herringbone patterns, have the added benefitof producing a substantial secondary flow, particularly along the axisof impeller rotation between cylindrical bearing surface 65 and impeller75, thereby minimizing stagnant flow between cylindrical bearing surface65 and impeller 75. Because stagnant areas may cause blood clots to formin blood pumps, the secondary flow reduces the chances of blood clotsforming. Further, asymmetrical herringbone patterns have the additionalbenefit over half herringbone patterns in that they provide similarradial stiffness as symmetrical herringbone patterns. As shown in FIG.10A-10D, each of the pattern grooves of internal surface 100 can beshaped in a variety of different manners, such as, but not limited to,rectangular grooves, rectangular grooves with a bevel, semi-circulargrooves, elliptical grooves, or the like. In other embodiments, impellerinternal surface 100 may also be a plain journal bearing without patterngrooves or a multi-lobe shape that creates a hydrodynamic bearing. Inalternative embodiments, the pattern grooves or multi-lobe shapes may belocated on the surface of cylindrical bearing surface 65 facing impeller75 rather than impeller internal surface 100 or the pattern grooves maybe located on an outer radial surface of impeller 75 or internal radialsurface of pump housing 15 facing the impeller 75.

FIG. 11 provides a cross-sectional side view of an illustrativeembodiment of housing 150 for pump 120. Similar to the embodiment shownin FIG. 2, pump 120 provides pump housing 150, impeller 125, shaft 130,hub 132, permanent magnets 135 and 140, motor housing 142, motor 145,and impeller chamber 160, which all provide a similar function to thecomponents discussed previously. These common elements may operate insubstantially the same manner as previously described. The substantialdifferences in the embodiments are discussed below.

The embodiment shown in FIG. 2 provided radial support of impeller 75utilizing a hydrodynamic bearing. However in FIG. 11, in addition to aradial hydrodynamic bearing, one or more external planar surfaces or topsurfaces 165 of impeller 125 include pattern grooves providing partialaxial hydrodynamic support.

FIG. 13 is a close up cross-sectional view of an area D of anillustrative embodiment of pump 120. Each arc shaped segment 127 ofimpeller 125 includes one or more pattern grooves on top surfaces 165.The pattern grooves on top surface 165 of impeller 125 and internalsurface 155 of housing 150 form a hydrodynamic bearing providing partialaxial hydrodynamic support that prevents or minimizes contact betweenimpeller 125 and housing 150. The pattern grooves on top surface 165 areconsidered to be interrupted because they are separated by the flowchannels of impeller 125.

Pattern grooves on top surface of impeller 125 may be any suitable typeof grooves including, but not limited to, spiral herringbone and spiralgrooves shown in FIGS. 12A and 12B. FIGS. 14A and 14B respectivelyprovide an isometric view of impeller 125 with spiral herringbone andspiral grooves. The arrangement of the pattern grooves on top surfaces165 is balanced so that instability during rotation of impeller 125 isprevented or minimized. For example, all of the top surfaces 165 havepattern grooves in the embodiment shown. However, it should berecognized that in other embodiments a balanced arrangement of topsurfaces 165 that have pattern grooves and do not have pattern groovesmay be utilized. A balanced arrangement of top surfaces 165 prevents orminimizes the instability of impeller 125. Examples of balancedarrangements for the embodiment shown may include, but are not limitedto, all top surfaces 165 with grooves or three alternating top surfaces165 with grooves and three without grooves. Flow inducing patterngrooves, such as spiral and spiral herringbone grooves, have the addedbenefit of producing a substantial secondary flow, particularly betweentop surface 165 of impeller 75 and internal surface 155 of housing 150.Additionally, various pattern groove types including symmetrical,asymmetrical, open, and/or dual groove patterns and various grooveshapes including rectangular, rectangular with a bevel, semi-circular,and elliptical shown in FIGS. 9A-9K and 10A-10D may be utilized. Anadditional benefit of the hydrodynamic bearing on top surface 165 ofimpeller 125 is that it increases impeller stability during rotation byrestraining angular motion along axes normal to the axis of impellerrotation.

FIG. 15 is a cross-sectional side view of an illustrative embodiment ofpump 170 with a conically shaped impeller 175. Many of the components ofpump 170 are substantially similar to the components of the previouslydiscussed illustrative embodiments. These similar components may operatein substantially the same manner as previously described. As in thepreviously discussed embodiments, impeller 175 is magnetically coupledto shaft 180 of motor 182. Permanent magnets 185 and 190 couple motor182 to impeller 175. However, in the embodiment shown, impeller 175 isformed in a generally conical shape. Top surfaces 195 of impeller 175facing internal surface 200 of the pump housing 202 are shaped in amanner that provides a hydrodynamic bearing between impeller topsurfaces 195 and internal surface 200.

FIG. 17 is a close up cross-sectional view of an area E of anillustrative embodiment of pump 170. As in the other embodimentspreviously discussed, internal surface 205 of impeller 175 may includepattern grooves for a hydrodynamic bearing providing radial support. Topsurfaces 195 of impeller 175 are angled to provide a generally conicalshaped impeller 175. FIGS. 16A-16E are views of various embodiments ofimpeller 175. Impeller 175 has multiple blade segments 210 that eachhave a top surface 195. Top surfaces 195 of blade segments 210 may belinear (FIG. 16A), convex (FIG. 16B), or concave (FIG. 16C) surfaces.Additionally, FIGS. 16D-16E are views of impeller 175 with convex andconcave top surfaces 195.

One or more of the top surfaces 195 of impeller 175 may incorporateinterrupted pattern grooves of any type including, but not limited to,spiral or spiral herringbone grooves. For example, the interruptedpattern grooves may be similar to the pattern grooves shown in FIGS. 12Aand 12B. The arrangement of the pattern grooves on top surfaces 195 isbalanced so that instability during rotation of impeller 175 isprevented or minimized. For example, all of the top surfaces 195 havepattern grooves in the embodiment shown. However, it should berecognized that in other embodiments a balanced arrangement of topsurfaces 195 that have pattern grooves and do not have pattern groovesmay be utilized. Flow inducing pattern grooves, such as spiral andspiral herringbone grooves, have the added benefit of producing asubstantial secondary flow, particularly between top surface 195 ofimpeller 175 and internal surface 200 of pump housing 202. Additionally,various pattern groove types including symmetrical, asymmetrical, open,and/or dual groove patterns and various groove shapes includingrectangular, rectangular with a bevel, semi-circular, and elliptical mayalternatively be utilized as shown in FIGS. 9A-9K and 10A-10D. In someembodiments, top surfaces 195 of impeller 175 do not utilize patterngrooves. For example, the conical shaped impeller 175 may be a pressurebalanced type impeller where the magnetic coupling formed by magnets 185and 190 provides sole axial restraint of impeller 175.

In addition to the axial restraint provided by the magnetic couplingdiscussed previously, the hydrodynamic bearing provided by top surfaces195 of impeller 175 partially restrains axial movement in the directionalong the axis of rotation. Because top surfaces 195 are angled, thehydrodynamic bearing of top surfaces 195 also partially restrains radialmotion of impeller 175. Thus, the hydrodynamic bearing of top surfaces195 provides partial radial and axial support for impeller 175. Thehydrodynamic bearings of top surface 195 and impeller internal surface205 and the partial restraint provided by the magnetic coupling increaseimpeller stability during rotation by restraining axial and radialmotion.

FIG. 18 is a cross-sectional side view of an illustrative embodiment ofpump housing 215 for pump 212. Many of the components of pump 212 aresubstantially similar to the components of the previously discussedillustrative embodiments. These similar components may operate insubstantially the same manner as previously described. As in thepreviously discussed embodiments, impeller 220 is magnetically coupledto shaft 225. Permanent magnets 230 and 235 couple the motor to impeller220.

Impeller 220 contains permanent magnets 240 and pump housing 215contains permanent magnets 245, 250 thereby forming a magnetic thrustbearing for minimizing axial movement of impeller 220. Permanent magnets245, 250 in housing 215 may be one or more magnets formed into a ring.FIG. 20 is a close up cross-sectional view of an area H of anillustrative embodiment of pump 212. Permanent magnets 240 in impeller220 and permanent magnets 245 in the top portion of pump housing 215 arearranged to provide a repulsive force between impeller 220 and pumphousing 215. Permanent magnets 240 in impeller 220 and permanent magnets250 in the bottom portion of pump housing 215 are also arranged toprovide a repulsive force between impeller 220 and pump housing 215. Theaxial restraint forces generated by magnets 240, 245, 250 aresignificantly greater than the attractive forces generated by thepermanent magnets 230 and 235 and thereby provide sole axial supportwith greater stiffness for impeller 220 during rotation. Magnets 240 inimpeller 220 and magnets 245, 250 in pump housing 215 provide largeaxial restraint forces to allow for increased clearances betweenimpeller 220 and pump housing 215 during rotation. The increasedclearances reduce damage to blood and allow for increased flow throughthe clearances during impeller rotation.

FIG. 19 is a cross sectional top view of an illustrative embodiment ofpump 212. Magnets 240 are arranged radially around impeller 220. Eachblade segment 255 of impeller 220 may provide an opening/region forreceiving one or more magnets 240. Additionally, in some embodiments,the top and/or bottom surfaces of impeller 220 may incorporate variouspattern groove types including spiral, spiral herringbone, symmetrical,asymmetrical, open, and/or dual groove patterns. Further, various grooveshapes including rectangular, rectangular with a bevel, semi-circular,and elliptical may also be utilized as shown in FIGS. 9A-9K and 10A-10D.

While the invention has been disclosed with respect to a limited numberof embodiments, those skilled in the art will appreciate numerousmodifications and variations can be made to those embodiments withoutdeparting from the scope of the appended claims.

1. A blood pump comprising: a pump housing, wherein the pump housingprovides an inlet, an outlet, and a bearing surface, wherein the pump isconfigured to move blood from the inlet to the outlet; an impellerhoused in the pump housing and having a plurality of blades joined by acentral ring having an internal surface, wherein the impeller isradially supported by a hydrodynamic bearing formed by the internalsurface and the bearing surface; and a hub configured to rotate about anaxis and comprising a first permanent magnet, wherein the impellercomprises a second permanent magnet located within the central ring, thefirst permanent magnet and the second permanent magnet (i) beingarranged to attract to each other in a radial direction perpendicular tothe axis, and (ii) forming a radial magnetic coupling to transmit torquefrom the hub to the impeller; wherein a maximum height of the pluralityof blades overlaps with each of the internal surface and the radialmagnetic coupling, the maximum height being in a direction of the axis.2. The blood pump of claim 1, wherein the blades are provided as anarray of arc shaped segments.
 3. The blood pump of claim 1, wherein theimpeller provides flow channels between circumferentially adjacent pairsof the plurality of blades.
 4. The blood pump of claim 3, wherein theflow channels have a maximum height that is substantially equal to themaximum height of the plurality of blades.
 5. The blood pump of claim 1,wherein the internal surface or the bearing surface provides at leastone row of pattern grooves.
 6. The blood pump of claim 1, wherein theinternal surface is substantially parallel to the bearing surface. 7.The blood pump of claim 1, wherein the internal surface is provided byan internal bore and the bearing surface is received within the bore. 8.The blood pump of claim 1, wherein the internal surface or the bearingsurface provides a multilobe shape.
 9. The blood pump of claim 1,wherein the pump housing comprises a non-ferromagnetic diaphragm thathouses the hub.
 10. The blood pump of claim 1, further comprising a rowof herringbone grooves on the internal surface or the bearing surface.11. The blood pump of claim 1, wherein the impeller is axially supportedby a magnetic thrust bearing comprising a third permanent magnetpositioned in the pump housing and a fourth permanent magnet positionedin the impeller.
 12. The blood pump of claim 11, wherein the fourthpermanent magnet positioned in the pump housing is ring shaped.
 13. Theblood pump of claim 11, wherein the third permanent magnet positioned inthe impeller is located within at least one of the plurality of blades.14. The blood pump of claim 1, wherein each of the first permanentmagnet and the second permanent magnet has a height in an axialdirection parallel to the axis, and the heights of the first permanentmagnet and the second permanent magnet overlap each other.
 15. The bloodpump of claim 1, wherein the impeller is an open type impeller orsemi-open type impeller.
 16. The blood pump of claim 1, wherein topsurfaces of the impeller provide a second hydrodynamic bearing for axialsupport of the impeller.
 17. The blood pump of claim 16, wherein the topsurfaces of the impeller provide at least one row of pattern grooves.18. The blood pump of claim 16, further comprising spiral grooves orspiral herringbone grooves on the top surfaces of the impeller.